Modelling Mean and Turbulence Fields in the Dry Convective Boundary Layer with the Eddy-Diffusivity/Mass-Flux Approach

The treatment of turbulence closure in atmospheric models is examined in the context of the dry convective boundary layer (CBL) and the eddy-diffusivity/mass-flux (EDMF) approach. The EDMF approach is implemented into a model called TAPM to use a coupled two-equation prognostic turbulence closure and the mass-flux approach to represent turbulence in the CBL. This work also extends the range of turbulence variables that can be derived from the mass-flux component of the model and uses these along with their values from the prognostic scheme to provide total turbulence fields that can be used to compare to data and/or to feed into other components of TAPM, including those needed to drive Eulerian and Lagrangian air pollution dispersion modules. Model results are presented for the afternoon of a simulated summer day and are compared to both laboratory and field observations in a mixed-layer scaled framework. The results show that the EDMF approach works well within TAPM and can provide good predictions of mean and turbulence fields, including in the upper levels of the CBL. The EDMF approach has several attractive features, including the potential to be one approach to unify the treatment of turbulence and dry and moist convection in atmospheric models.